It's the latest fatal shooting involving the assault weapon, including Sandy Hook, the Texas church shooting, the Route 91 Harvest Music Festival shooting and at the Pulse nightclub in Orlando. Here's why:

(Photo: Instagram @nikolascruzmakarov)

The National Rifle Association considers AR-15-style rifles the best-selling gun in the U.S., with Americans owning over 8 million of them. Although they have been labeled "assault rifles," the National Shooting Sports Foundation wants them to be more widely known as "modern sporting rifles," arguing that, "If someone calls an AR-15-style rifle an 'assault weapon,' he or she either supports banning these firearms or does not understand their function and sporting use, or both."

Many gunmakers produce rifles that are like AR-15s, but are not actually an AR-15. The "AR" stands for ArmaLite and the name is owned by Colt, notes USA Today. The patent on the rifle's operating system ran out, so other companies have made similar weapons.

The NRA says the AR-15 is "customizable, adaptable, reliable and accurate," which is just one reason why it is popular. The weapon can be used for "sport shooting, hunting and self-defense situations," so you can "personalize" the weapon. It is also accurate and lightweight, plus you can add high-capacity magazines to the rifles. The 30-round magazine is common for modern sporting rifles, although some states have limits on magazine sizes.

Cruz is only 19 years old, and bought his weapon when he was 18. It was perfectly legal for him to buy a Smith & Wesson M&P 15 rifle in February 2017 from Sunrise Tactical Supple in Coral Springs, reports the Sun Sentinel. However, it would have been illegal for him to purchase a handgun.

That is due to the Gun Control Act of 1968, which raised the federal handgun purchase age limit to 21. At the time, rifles like AR-15s were not widely available. "Handguns were far, far more common and assault rifles had not reached the market saturation that they have today," Avery Gardiner, co-president of the Brady Campaign to Prevent Gun Violence, told Slate Friday.

Congress did pass a federal assault weapons ban in 1994, but when it expired 10 years later, the Republican-controlled Congress let the ban expire. As the Associated Press reported at the time, the ban outlawed 19 types of military-style weapons, including the Colt AR-15.

According to USA Today research, AR-15-style rifles were used by James Holmes at the 2012 shooting in an Aurora, Colorado movie theater; Adam Lanza at the Sandy Hook Elementary School Shooting in 2012; John Sawahri when he killed five people at a Santa Monica, California home in 2013; Omar Mateen at the 2016 Pulse nightclub shooting in Orlando. Florida; and Devin Kelly at a Springs, Texas church in November 2017.

Stephen Paddock also had an AR-15-style rifle among the weapons he used at the Las Vegas mass shooting in October 2017.